Thanks for the suggestions. Not too new to power tools, but most of the work I do is with metal. If we decide to remove that strip of osb I think I will work it out with a backsaw and chisel.
Anyway, the carpeting with pad measures about 1 inch thick and sits on top of the same OSB that is around the edges of my bathroom. Am I incorrect that the thinset + cement board + morter + tile = 1 inch? The hardiboard that I looked at was 3/8th inch thick. I didnt measure the ceramic tile, but it looks like its also about 3/8th thick. With the thinset and morter, this would be about 1inch and would put the top of the tile pretty close, but maybe a hair higher than the carpet. Could we also use the thiner cement board in case we want the tile a little lower or must tile go over at least 1/2 inch hardiboard?
The flooring in the house is 1.125 inch tongue/groove ply on top of joists. Then there is 1/2 inch osb on top of this. Finally carpet with pad on top of the osb. The bathroom originally had half carpet and half linoleum. We have ripped all this up and cut most of the osb out.